Wound healing is a dynamic pathway that optimally leads to restoration of tissue integrity and function. A “chronic” wound is one in which the healing process is prolonged and incomplete, resulting in a lack of restoration of integrity. Chronic wounds are a challenge to the patient, healthcare professionals, and the healthcare system, and significantly impair the quality of life for millions of people. Long-term, repetitive treatment is required, which imparts an enormous burden on society in terms of lost productivity and healthcare budgets.
Hard-to-heal (HTH) or chronic ulcers are a class of chronic wound. HTH ulcers of the leg and the foot, are often painful, stigmatising and have a negative impact on functional ability.
Venous leg ulcers (VLUs) are chronic skin and subcutaneous ulcerations that occur on the lower leg, between the knee and the malleolus. The Swedish Medical Product Agency defines a VLU as one that is below the knee caused by venous insufficiency, which does not heal within six weeks of standard therapy (i.e. traditional wound care products, such as low technology gauze-based dressings, woven and non-woven sponges, conforming bandages and non-adherent bandages).
Chronic venous insufficiency (CVI) results when the veins in the legs lose the ability to pump venous blood effectively. A range of problems result from leakage of fluid into the interstitial space and the area is then prone to ulceration.
VLUs constitute the majority of all leg ulcers accounting for 70-90% of wounds in lower extremities (see Snyder, Clin. Dermatol., 23, 388 (2005)). Epidemiological data suggests that 1.5-3.0 people per 1,000 (0.15-0.3%) have active leg ulcers, rising to around 20 people per 1,000 (2%) in individuals over 80 years of age (see Valencia et al, J. Am. Acad. Dermatol., 44, 401 (2001)). Consequently, VLUs are a massive economic burden. In Europe alone, the total annual cost is estimated at €6.5 billion based on an average cost of €7000 per episode (see Posnett, et al, J. Wound Care, 18, 154 (2009)). Expense is not limited solely to the direct cost of ulcer care, but includes indirect costs associated with disability and lost days at work.
Diabetic foot ulcers (DFUs) are one of the major complications in patients suffering from diabetes mellitus. Diabetes causes peripheral neuropathy with impaired sensory function and an increased risk of wounding. Circulatory impairment impedes the process of natural skin healing thereby resulting in HTH wounds. The risk of a patient with diabetes mellitus developing a foot ulcer is approximately 25% according to the International Diabetes Federation (see e.g. Boulton et al, Lancet, 366, 1719 (2005) and Singh et al, JAMA, 293, 217 (2005)). The annual incidence and prevalence of diabetic foot ulcers in patients with diabetes are 2-6% and 4-10%, respectively (see also Ramsey et al, Diabetes Care, 22, 382 (1999)). In addition, 10% of diabetic patients have contributing factors such as peripheral neuropathy and vascular complications for developing foot ulcers. DFUs are prone to infections leading to significant morbidity, and are associated with 25-90% of all amputations in this patient population (see also Ragnarson-Tennvall et al, Diabetologia, 44, 2077 (2001)).
DFUs also represent a significant economic burden. In Europe, DFUs that do not heal within 12 months cost an average of €20,000 per patient (Prompers et al, Diabetologia, 51, 1826 (2008)).
There is no evidence to support that standard dressing materials are of any significant benefit to treat the aforementioned HTH ulcers, even when used in conjunction with other standard measures (cleansing, debridement, bandaging, etc.). In Europe, Regranex® (becaplermin) gel is indicated for the treatment of lower extremity diabetic neuropathic ulcers that extend into the subcutaneous tissue or beyond and have an adequate blood supply. It is used as an adjunct to, and not a substitute for, good ulcer care practices including initial sharp debridement, pressure relief and infection control. Although Regranex is the only drug product approved for treatment of such HTH ulcers, it has no documented effect on VLUs.
Thus, there is an urgent need for improved treatments of chronic wounds, and in particular HTH ulcers such as VLUs and DFUs.
LL-37 is derived from the 18-kDa human cathelicidin antimicrobial protein 18 (hCAP18). It is an important mediator in tissue repair and defense against infection. Both hCAP18 and LL-37 are present in various body fluids, including wound fluid (see, for example, Murakami et al, J. Dent. Res., 81, 845 (2002), Schaller-gals et al, Am. J. Respir. Crit. Care Med., 165, 992 (2002) and Sørensen et al, J. Biol. Chem., 278, 28540 (2003)). Although, in acute wounds, transcription of hCAP18/LL-37 is up-regulated within a few hours, and LL-37 is expressed at the wound margin by basal epidermal keratinocytes, chronic wounds have no LL-37 immunoreactivity at the wound edge (see, for example, Dressel et al, Exp. Dermatol., 19, 628 (2010) and Rivas-Santiago et al, J. Derm. Sci., 65, 19 (2012)).
In vivo studies with synthetic LL-37 have shown that subcutaneous injection stimulates angiogenesis (Koczulla et al, J. Clin. Invest., 111, 1665 (2003)), and repeated topical administration in acute wounds attracts inflammatory cells to the surrounding tissue. Antibodies against LL-37 inhibited healing in an ex vivo model of human acute wounds (Heilborn et al, J. Invest. Dermatol., 120, 379 (2003); see also international patent application WO 2004/067025), while topical treatment with LL-37 stimulated wound healing in mice treated with a corticosteroid to impair normal healing (Ramos et al, Peptides, 32, 1469 (2011)). Administration of LL-37 in acute wounds of diabetic mice with impaired wound healing has shown beneficial effect in one study (Carretero et al, J. Invest. Dermatol., 128, 223 (2008)), while other studies have failed to show an effect (Steinstraesser et al, PLoS ONE, 7, e39373 (2012)). EP 1 358 888 discloses that LL-37 is an inducer of angiogenesis.
International patent application WO 2009/001087 discloses wound care products in which LL-37 is impregnated into a solid substrate (a dressing) comprising a wound care material. There is no suggestion in that document that it is necessary to apply a certain dose of LL-37 in a formulation per unit wound area to treat the wound effectively. There is certainly no suggestion that there may be an upper limit to that dose, let alone what that limit might be.